1. Field of the Invention
The present invention relates to a method for producing toner particles that are used in order to form toner images through development of an electrostatic latent image that is formed in accordance with a method such as an electrophotographic method, an electrostatic recording method or a toner jet recording method.
2. Description of the Related Art
A requirement of lower power consumption has been placed in recent years on printers and copying machines, while toner is required to exhibit ever better performance. Printers and copying machines must also be amenable to use, without problems, under various environments, and toner is required to have improved heat-resistant storability, and, at the same time, exhibit no changes in performance on account of storage.
To meet these both requirements it becomes necessary to solve the trade-off inherent in suppressing changes in physical properties during high-temperature storage while permitting softening of the toner.
To that end, toners have been studied in which a crystalline resin having excellent response speed to heat is added to the toner. However, simple addition of a crystalline resin entails not only instances of worsened heat-resistant storability of the toner, but also instances where the degree of crystallinity of the crystalline resin changes on account of high-temperature storage, and the performance of toner is impaired as a result. Accordingly, toners have been proposed in which various approaches are resorted to with a view to bringing out the characteristics of the crystalline resin. One such approach involves specifically leaving the crystalline resin for a prolonged period of time at a temperature lower than the melting point of the crystalline resin, to elicit as a result growth of crystals in the crystalline resin, enhance heat-resistant storability, and suppress changes in degree of crystallinity derived from high-temperature exposure.
Japanese Patent Application Publication No. 2006-065015 proposes a toner production method comprising a step of storing a toner that contains a crystalline resin, at a temperature ranging from 45° C. to 65° C. In the above toner production method, however, part of the toner may aggregate as a result of the step of storing the toner at that temperature. Since the above step is carried out in accordance with a dry scheme, the method was also problematic owing to concerns regarding image density, and otherwise poorer developing performance of the toner, on account of the occurrence of the phenomenon whereby the crystalline resin that is present in the vicinity of the toner surface migrates into the toner surface accompanying crystal grow.
Japanese Patent Application Publication No. 2009-128652 proposes a toner wherein a crystalline polyester is added to a non-crystalline polyester, and a thermal treatment is carried out at a specific temperature that is lower than the melting point of the crystalline polyester. In the above toner, the non-crystalline polyester is used in a binder resin, and hence the crystalline polyester is compatibilized with the binder resin in the production process of the toner. As a result, not only did the improvement efficiency of degree of crystallinity in a subsequent heating treatment drop very significantly, but also instances arose wherein some of the components remained compatibilized, and sufficient heat-resistant storability failed to be obtained.
Japanese Patent Application Publication No. 2012-2833 proposes a toner production method comprising a step of holding a suspension-polymerized toner that contains a crystalline resin at a temperature that is lower than the melting point of the crystalline resin, during a production process. In the above toner, the binder resin and the crystalline resin constitute a non-compatible system. In some instances, therefore, the dispersion state of the crystalline resin in the toner did not readily become homogeneous, even if the degree of crystallinity was improved from that state, and sufficient low-temperature fixability and sufficient heat-resistant storability failed to be achieved concomitantly.
Such being the case, various approaches have been proposed in order to suppress adverse effects on the storability of toners into which a crystalline resin is introduced, while sufficiently bringing out the fixing performance that is elicited by adding a crystalline resin. However, no toner production method has been yet proposed in which sufficient performance is effectively achieved.